Driving and control mechanisms for power-operated machine tools



R. C. CLERK Jan. 19, 1965 DRIVING AND CONTROL MECHANISMS FOR POWER-OPERATED MACHINE TOOLS Filed July 12, 1962 m w mwzmomm m3 m \a v N WWW I: M I M yv ZOFUMEQ QZVEOB I11- momwummzou Q mojm mm 5:25 :2: ym ml \NVENTOR ROBERT C. CLERK Y 1M audiwfiq ATTORNEYS United States Patent 3,165,979 DRIVING AND CONTROL MECHANISMS FGR PGWER-OPERATED MACHENE T053113 Robert Cecil Clerk, 97 High St, Maidenhead, 1 Berkshire, England Filed July 12, 1962, Ser. No. 2ll9fi37 3 Claims. (Cl. 9l--32l) This invention relates to driving and control mecha nism for power-operated machine tools, of the types which incorporate a power operated slide or work table operated by means of a hydraulic power cylinder. Where the thrust required to be imparted to the slide is of a high order, for example 63,000 lbs., the speed of travel of the slide is usually arranged to be limited to a relatively low value, since with the thrust requirement of the above example, every one foot per minute in the speed of the slide would involve an expenditure of 1 horsepower by the hydraulic pump that feeds the power cylinder and by the pump driving means, which is normally an electric motor.

It is also well known that when working certain metals, either by cutting or by direct plastic deformation, there are well defined separated high slide speeds at which other economic factors, for example improved tool life, show to advantage. These factors are however of minor importance in comparison with the greatly increased bulk and capital cost of the mechanism normally required for achieving these high speeds,

The object of the present invention is to provide slide control mechanism which permits high slide speeds with little or no increase in bulk or capital cost.

Accordingly the invention provides a driving and control mechanism of the type referred to in which the power cylinder is arranged to 'act as a pressure accumulator in addition to its normal driving function.

From another point of view the invention provides a driving and control mechanism of the type referred to, in which the power cylinder is arranged to contain a hydraulic liquid to one side. of the piston for effecting the movement of the slide in a non-working direction, and a substantially enclosed volume of gas on the other side of the piston for elfecting the movement of the slide in a working direction. a

The slide movement in the non-working direction may be conveniently slow, the power being accumulated in the gas for a rapid return stroke i.e., the working stroke.

A large capacity, low resistance path is provided for the hydraulic liquid expelled from the cylinder during the working stroke, controlled by a large capacity adjustable valve. The large capacity valve is adjustable to control the back pressure applied to the piston to decelerate the same. i

The hydraulic liquid pressure may be supplied by a pump through a restricted pipe, the restriction being bypassed by a one way valve, or the restriction may be incor-porated in a foot valve of known construction.

The length of the stroke may be controlled by stroke limit controls, actuated by the slide, for altering the setting of the large capacity valve to supply the required arresting back pressure.

The speed of the working stroke may be controllable by adjustment of the air pressure acting on the piston.

These and other parts of the invention are embodied in a preferred form of driving and control system which will be described with reference to the accompanying drawings in which:

FIG. 1 is a schematic diagram of the system.

FIG, 2 is a section through the back pressure valve in the direction of the arrow A of FIG. 1.

In a driving and control system of the type referred to, the piston rod 1 of the piston of the power cylinder 2 projects through the cylinder at one end and is drivably 3,165,979 Patented Jan. 19, 1965 connected to a transverse projection on the slide 3. On the piston rod side of the piston the cylinder is connected to a pressure air receiver 4 which is a substantially closed chamber connected to a compressor 4a for replenishing leakages, and on the other side of the piston the cylinder is connected via aback pressure control valve 5 to a reservoir '23 and also a motor driven pump 6. The back pressure control valve 5 comprises a slide 7 movable transversely across the end of the cylinder relative to a fixed valve body 8, the slide 7 having a circular aperture 9 which during movement of the slide registers to varying extents with a circular aperture 10 in the valve body. At one end of the slide '7 is provided a pilot plunger 11 which projects from the slide in the direction of movement of the slide into a valve pilot oil-cylinder 12 which is connected by a pipe 12a to the oil-containing space 13 of the power cylinder 2. At its other end the slide has a pilot plunger 14 which projects from the slide in the direction of movement thereof into a valve pilot air cylinder '15 which is connected through a pipe 15a via a speed control valve 16 to an air pressure system and also via stroke limit control valve .17 actuated by a control :18 which is disposed so as to be engaged by a projection 19 on the slide 3 as it approaches the end ofits working stroke.

A valve 20 is included in the oil line 6:: from the pump 6 to the cylinder 2 and is operated by a solenoid 21 controlled by a return limit switch 22 actuated by a projection 29 of .the slide 3 toward the end of its non-working stroke. The valve 20 connects the oil line 611 to either the pump 6 or to the oil reservoir 23 and the oil line includes a restriction 24.

The above-mentioned restriction 24 is bypassed by a non-return valve 25 which opens in the direction to enable full pump pressure to be applied to the oil space 13 of the power cylinder 2, but closes in the other direction, so that during movement of the power piston 1 in the working direction the oil must flow to the reservoir 23 via the restriction 24. At the commencement of the nonworking stroke the oil space 13 of the power cylinder is sealed except to the pump delivery which therefore serves to return the power piston l, and with it the machine slide 3 to the right from the position shown in FIG. 1, against the air pressure in the receiver 4 and in so doing restores the air pressure therein, so that the horsepower of the hydraulic pump 6 and the electric motor driving it are determined only by thrust pressure and the return speed of the slide 3. When the power piston 1 nears the end of its non-Working stroke the feed from the pump 6 is automatically cut off when projection 29 contacts limit switch 22 and since during this stroke the full pressure of the air in the receiver 4 is maintained on. the plunger 14 of the valve pilot air cylinder 15 the machine slide 3 will be ready for the start of the next working stroke, which is initiated by relieving pressure from the said plunger 14 as by an exhaust valve and manual push button (not shown) so that the other pilot plunger 11 which is subject to the oil pressure in the power cylinder 2 will fully open the back pressure control valve 5 so as to cause the aperture 9 therein to register fully with the aperture 16 in the valve body and so allow maximum acceleration of the machine slide 3 to the left in FIG. 1 up to the preset speed at which the speed control valve 16 takes charge to maintain the set speed by controlling the effective aperture of the back pressure valve 5.

Towards the end of the working stroke of the slide 3, the stroke limit projection 19 operates control 18 to actuate the stroke limit control valve 17 to admit full available air pressure to the air pilot plunger 14-, tending to close the back pressure control valve 5 against the rising back pressure of oil acting on the other plunger 11, so that the valve will assume 'a balanced condition to provide a back pressure in the space 13. For the valve to remain in san ers must gradually close to decrease the. area of the port 10 available for the out-flow of oil, until the valve is fully closed.

If the machine is're-set for a lower slide speed, then unless the stroke limit control valve 17 or the controlling air pressure were suitablyadjusted, with consequent risk of non-readjustment when resetting the machine to higher speed, the slide 3 would stop short at a distance from the end of its working stroke which is inversely propon tional to the square of the speed when retardation of the slide commences, and it is to obviate this that the restricted bleed (restriction 24) has been introduced together with a spring or equivalent means (not shown) serving as a cushioned stop for the slide.

The monitoring pressure which is used for controlling the back pressure'control valve 5 may be hydraulic pressure derived from a pump, but for high speed ope ation it has been found that air pressure as described provides quicker and more stable control response; The compressed air providing this pressure may be derived from a separate pressure system as described or from the main receiver referred to.

Theback pressure control yalve 5 will be subjected to considerable thermal eifects when retarding the slide 3 and this may tend to distort the valve making it sluggish or inoperable, and it has been found that a semi-rotary well as having much lower flow loss in the fully open position,

Since after the system has accelerated its speed potential is limited only by the maximum hydraulic back pressure, it is important for very high speed operation that the back pressure control valve 5 and the piping 26 connecting it on the one hand to the power cylinder 2 and on the other hand to the oil reservoir 23 should be designed for minimum flow loss in the fully open condition. The piping may therefore be of substantially the same bore as the open end of the cylinder 2, viz., the end at which the back pressure control valve 5 is provided, with sweeping bends 27 at changes of direction and an end 28 in the oil reservoir 23 which is scarfed or divergent or is formed to provide flow splitters so as to reduce out-flow shock, disturbance and back pressure.

space of the power cylinder and the reservoir may be incorporated in :a foot valve of known construction.

it is to be understood that the invention is not restricted to the exact details shown and described but embraces such modifications as come within the ambit of the accompanying claims.

. I claim:

1. A driving and control mechanism for power operated machine tools comprising a power operated slide, a hydraulic power cylinder, a piston within the cylinder connected to and operating the slide, an hydraulic liquid circuit connected to the power cylinder so as to feed liquid under pressure to one side of the piston for effecting the movement of the slidein a non-working direction, and a substantially enclosed chamber for gas under pressure connected to the cylinder to apply gas to the other side of the piston for effecting the movement of the slide'in a working direction, means for controlling the speed of the working stroke of the slide by adjustment of air pressure in said enclosed chamber, a large capacity low resistance path being provided for hydraulic liquid expelled from the cylinder during a working stroke, a valve 'openable to full bore sizeof the cylinder located in said low resistance path for controlling the flow of liquid in the path, and means for adjusting said valve to control the back pressure applied to the piston to eifect deceleration thereof towards the end of a working stroke.

2. A driving and control mechanism according to claim 1 in which said means for adjusting said valve to control the back pressure comprises a stroke limit control valve actuated by movement of the slide.

3. A driving and control mechanism according to claim 1 including a pump connected to the cylinder for supply of liquid by a path in which there is a restriction and a one-way valve, said one-way valve by-passing the said restriction.

References Cited in the file of this patent UNITED STATES PATENTS 1,460,586 Howse July 3, 1923 2,669,840 Joy Feb. 23, 1954 2,787,123 Delvaux Apr. 2, 1957 2,790,340 Cross Apr. 30, 1957 2,827,764 Simmonds Mar. 25, 1958 2,870,789 Bilaisis Jan. 27, 1959 

1. A DRIVING AND CONTROL MECHANISM FOR POWER OPERATED MACHINE TOOLS COMPRISING A POWER OPERTED SLIDE, A HYDRAULIC POWER CYLINDER, A PISTON WITHIN THE CYLINDER CONNECTED TO AND OPERATING THE SLIDE, AN HYDRAULIC LIQUID CIRCUIT CONNECTED TO THE POWER CYLINDER SO AS TO FEED LIQUID UNDER PRESSURE TO ONE SIDE OF THE PISTON FOR EFFECTING THE MOVEMENT OF THE SLIDE IN A NON-WORKING DIRECTION, AND A SUBSTANTIALLY ENCLOSED CHAMBER FOR GAS UNDER PRESSURE CONNECTED TO THE CYLINDER TO APPLY GAS TO THE OTHER SIDE OF THE PISTON FOR EFFECTING THE MOVEMENT OF THE SLIDE IN A WORKING DIRECTION, MEANS FOR CONTROLLING THE SPEED OF THE 